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Re: "Cope's Rule" Put to the Test



In a message dated 97-01-27 14:47:17 EST, ornstn@inforamp.net (Ronald
Orenstein) writes:

<< At 10:36 PM 1/26/97 -0500, George Olshevsky writes:
 Name a tetrapod family or other clade most of whose included
 >genera and species are of a >significantly< smaller adult size (factor of
two
 >or more) than its earliest-known member or hypothesized common ancestor.
For
 >every one you name of the latter, I'll name three that show the opposite
 >trend.>>

As per an earlier post, I note that the commonest size change within a clade
is >none<; that is, there is no significant change in size from a common
ancestor to its more immediate descendants--a random small jump up or down,
perhaps. But when size change does occur, particularly over the long term, it
tends to go in the direction of size increase rather than size decrease: That
is, the "random jumps" tend to be "up" rather than "down." As Tom Holtz has
just pointed out, this may simply be due to the open-endedness of
enlargement. But if we use the >logarithm< of the size increase or decrease,
rather than simply the increase itself, to establish significance, we can
expand the available lower end to infinity and make decrease as open-ended as
size increase. Of course, an organism can scarcely evolve into forms smaller
than its own cells...
 
<< Dendrobatid frogs>>
Plesiosaurs
Mosasaurs
Varanid lizards

<< Pygmy chamaeleons (I think)>>
Plateosauridae
Segnosauria
Ornithopoda

<< hummingbirds>> -- I'm pretty doubtful about this one; I wouldn't consider
hummingbirds significantly smaller than what might have been their common
ancestor--but okay
Ratite birds
Tyrannosauridae
Teratorns

<< Passeriformes>>
Sauropoda
Stegosauria
Ceratopia

<< hyraxes>>
Proboscidea
Titanotheriidae
Rhinocerotidae

<< dwarf lemurs >>
Hominidae
Great apes
Equidae (as far as I know, all known horses are bigger than _Hyracotherium_)